1. Field of the Invention
The present invention relates to a dielectric ceramic composition, an electronic device and production methods of them, and particularly relates to a nonreducing temperature compensating dielectric ceramic composition preferably used for an electronic device, such as a multilayer ceramic capacitor, using a base metal as an internal electrode thereof.
2. Description of the Related Art
Multilayer ceramic capacitors are widely used as electronic devices, and the number used in one electronic device is also large. A multilayer ceramic capacitor is normally produced by stacking an internal electrode layer paste and a dielectric layer paste by a sheet method or a printing method, etc. and cofiring the result.
A dielectric ceramic material used for a multilayer ceramic capacitor, etc. of the related art has a property of getting reduced and becoming a semiconductor when fired in a reducing atmosphere. Therefore, as an internal electrode material, Pd and other precious metals, which do not melt at a temperature of sintering the dielectric ceramic material and are not oxidized even if fired under a high oxygen partial pressure of not bringing the dielectric ceramic material to be a semiconductor, have been used.
However, high prices of Pd and other precious metals have hindered a cost reduction of the multilayer ceramic capacitor much. Thus, use of relatively inexpensive base metals, such as Ni and a Ni alloy, as the internal electrode material has become dominant.
When using a base metal as a conductive material of the internal electrode layer, however, the internal electrode layer is oxidized when fired in the air. Accordingly, cofiring of the dielectric layer and internal electrode layer has to be performed in a reducing atmosphere.
However, when fired in a reducing atmosphere, the dielectric layer is reduced and the insulation resistance becomes low. Therefore, a nonreducing dielectric material has been proposed. But again, a multilayer ceramic capacitor using a nonreducing dielectric material has a disadvantage that the insulation resistance (IR) becomes poor when a thickness of the dielectric layer is made thin (5 μm or thinner) according to a reliability test.
On the other hand, demands have become stronger for a temperature compensating dielectric ceramic composition, wherein a temperature change of the capacitance is small, that is the capacitor-temperature coefficient is small, and able to be freely controlled in a range of −50 to +150 ppm/° C., so that a ceramic material capable of providing such a capacitor having a controllable low temperature coefficient has become necessary.
Note that, as described in the Japanese Patent Publication No. 2997236, there has been a proposal of a highly reliable nonreducing dielectric ceramic composition able to be sintered at 1300° C. or lower, wherein a temperature coefficient of the capacitance is small and able to be freely controlled in a range of −15 to +150 ppm/° C., the insulation resistance at 25° C. is 1×1013 Ω or higher, the specific permittivity and dielectric loss tangent (tan δ) have a little frequency dependency, and accelerated lifetime of the insulation resistance is long even when the insulation layer is made thin. The dielectric ceramic composition is preferably used for a multilayer ceramic capacitor using a base metal, such as Ni, as an internal electrode.